Effects of an extract of Ginkgo biloba and diverse substances on the phasic and tonic components of the contraction of an isolated rabbit aorta.

1. The effects of phentolamine, propranolol, D 600, theophylline, papaverine and an extract of Ginkgo biloba were studied with respect to the two phases of the contractile response induced by norepinephrine in an isolated rabbit aorta. 2. Phentolamine (3 x 10(-6) M) inhibits the rapid phase of the contraction of the rabbit aorta brought on by norepinephrine (NE) 10(-5) M more strongly than the tonic phase. Propranolol (10(-6) M) potentiates this rapid phase. 3. D 600 inhibits the slow phase with an EC50 = to 3.8 x 10(-8) M. 4. Papaverine and theophylline increase the relaxation that follows the rapid phase of contraction. The slow phase is inhibited only by papaverine. 5. The extract of Ginkgo biloba (Gb) at a concentration of 3 mg/ml has the same type of effect as papaverine 3 X 10(-5) M.